build: modernize repo-lens skeleton and cross-platform configuration

Replace CPM with FetchContent and update GoogleTest to v1.18.0.
Add compiler toolchains and Debug, Release, and sanitizer presets.
Require CMake 4.0, use target properties for compiler settings,
and enable compilation database export.

Fix skeleton compilation errors and adopt trailing return types,
nodiscard execute methods, and noexcept signatures. Update CI
and project documentation without implementing any TODOs.

Validated Windows builds and tests in all three configurations.

cmake/gtest.cmake

@@ -1,17 +1,20 @@
 include_guard()
 
-CPMAddPackage(
-	NAME googletest
-	GITHUB_REPOSITORY google/googletest
-	GIT_TAG v1.13.0
-	VERSION 1.13.0
-	OPTIONS
-	"INSTALL_GTEST OFF"
-	"gtest_force_shared_crt ON"
+include(FetchContent)
+
+set(INSTALL_GTEST OFF CACHE BOOL "Install GoogleTest" FORCE)
+set(gtest_force_shared_crt ON CACHE BOOL "Use the shared MSVC runtime for GoogleTest" FORCE)
+
+FetchContent_Declare(
+	googletest
+	GIT_REPOSITORY https://github.com/google/googletest.git
+	GIT_TAG v1.18.0
+	GIT_SHALLOW TRUE
 )
+FetchContent_MakeAvailable(googletest)
 set_property(TARGET 
 	gtest 
 	gtest_main 
 	gmock
 	gmock_main
-	PROPERTY FOLDER third_party/GoogleTest)
+	PROPERTY FOLDER third_party/GoogleTest)